Chapter 16 Creating UFS, TMPFS, and LOFS File Systems (Tasks)

This chapter describes how to create UFS, temporary (TMPFS), and loopback (LOFS)
file systems. For UFS file systems, this chapter shows you how to create a file system
on a hard disk by using the newfs command. Because TMPFS and LOFS
are virtual file systems, you actually “access” them by mounting them.

Creating a UFS File System

Before you can create a UFS file system on a disk, the disk must be formatted
and divided into slices. A disk slice is a physical subset of a disk that is composed
of a single range of contiguous blocks. A slice can be used either as a raw device
that provides, for example, swap space, or to hold a disk-based file system. See Chapter 10, Managing Disks (Overview) for
complete information on formatting disks and dividing disks into slices.

Volume management products, like Solaris Volume Manager, create more sophisticated volumes, that expand beyond single slice or single disk boundaries. For
more information about using volumes, see Solaris Volume Manager Administration Guide.

Note –

Solaris device names use the term slice (and the letter s in
the device name) to refer to the slice number. Slices are also called “partitions.”

You need to create UFS file systems only occasionally, because the Solaris operating system automatically
creates them as part of the installation process. You need to create (or re-create)
a UFS file system when you want to do the following:

Add or replace disks

Change the existing partitioning structure

Do a full restoration of a file system

The newfs command is
the standard way to create UFS file systems. The newfs command
is a convenient front-end to the mkfs command, which actually creates
the new file system. The newfs command reads parameter defaults,
such as tracks per cylinder and sectors per track, from the disk label that will contain
the new file system. The options you choose are passed to the mkfs command
to build the file system.

Default Parameters for the newfs Command

To make a new file system on a disk slice, you almost always use the newfs command. The following table shows the default parameters that are
used by the newfs command.

Parameter

Default Value

Block size

8 Kbytes

Fragment size

1 Kbyte

Minimum free space

((64 Mbytes/partition size) * 100), rounded down to the nearest integer and
limited to between 1% and 10%, inclusively

Displays what parameters the newfs command would
pass to the mkfs command without actually creating the file system.
This option is a good way to test the newfs command.

-bsize

Specifies the block size for the file system, either 4096 or 8192
bytes per block. The default is 8192.

-ibytes

Specifies the number of bytes per inode. The default varies depending
on the disk size. For more information, see newfs(1M).

device-name

Specifies the disk device name on which to create the new file system.

The system asks for confirmation.

Caution –

Be sure you have specified the correct device name for the slice before
performing this step. If you specify the wrong slice, you will erase its contents
when the new file system is created. This error might cause the system to panic.

To verify the creation of the UFS file system, check
the new file system.

# fsck /dev/rdsk/device-name

The device-name argument specifies the name of the
disk device that contains the new file system.

See Also

Creating a Temporary File System (TMPFS)

A temporary file system (TMPFS) uses local memory for file system reads and
writes, which is typically much faster than reads and writes in a UFS file system.
TMPFS file systems can improve system performance by saving the cost of reading and
writing temporary files to a local disk or across the network. Files in TMPFS file
systems do not survive across reboots or unmounts.

If you create multiple TMPFS file systems, be aware that they all use the same
system resources. Files created under one TMPFS file system use up the space available
for any other TMPFS file system, unless you limit TMPFS sizes by using the -o size option of the mount command.

Example 16–3 Mounting a TMPFS File System at Boot Time

You can set up the system to automatically mount a TMPFS file system when it
boots by adding an /etc/vfstab entry. The following example shows
an entry in the /etc/vfstab file that mounts /export/test as a TMPFS file system when the system boots. Since the size=number option is not specified, the size of the
TMPFS file system on /export/test is limited only by the available
system resources.

Creating a Loopback File System (LOFS)

A
LOFS file system is a virtual file system that provides an alternate path to an existing
file system. When other file systems are mounted onto an LOFS file system, the original
file system does not change.

Example 16–5 Mounting an LOFS File System at Boot Time

You can set up the system to automatically
mount an LOFS file system when it boots by adding an entry to the end of the /etc/vfstab file. The following example shows an entry in the /etc/vfstab file that mounts an LOFS file system for the root (/) file system on /tmp/newroot.

/ - /tmp/newroot lofs - yes -

Make sure the loopback entries are the last entries in the /etc/vfstab file. Otherwise, if the /etc/vfstab entry for a loopback
file system precedes the file systems to be included in it, the loopback file system
cannot be mounted.